Sucker rods

ABSTRACT

The disclosure relates to a sucker rod assembly for use in an oil well. The sucker rod assembly includes an elongated hollow rod having a threaded section at an end, a tubular connector having a threaded section at one end for engaging with the threaded section of the elongated hollow rod, and a second threaded section at the other end, and a tubular coupling having a threaded section at each end for engaging with the second threaded section of said tubular connector and with a second tubular coupling or sucker rod. The hollow rod, connector and coupling form a continuous hollow core for carrying fluid, cables, fiber optics or other materials.

CLAIM FOR PRIORITY

This application claims the benefit of priority to U.S. Provisional Application No. 62/676,066, filed May 24, 2018, the contents of which are hereby incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present invention relates to sucker rods used in the oil industry, in particular although not exclusively to hollow rods that allow the external insertion of a fluid, sensors and other devices.

BACKGROUND

In a producing oil well fluid is pushed to the surface through the well bore by the internal pressure of the reservoir. If reservoir pressure is not strong enough, artificial lift methods must be used to move fluids from the reservoir to the surface.

The most common type of artificial lift applied is the sucker rod pumping system. A sucker rod pumping system uses a surface power source, pump arrangement and rod string to drive a pump assembly submerged in the fluid near the bottom of the well. It comprises several components some of which operate on the surface and other parts operate in the well bore.

A beam and crank assembly on the surface is connected to a series of interconnected sucker rods commonly referred to as a sucker rod string is run down into the wellbore though the production tubing extending down through the well. The sucker rod string is connected to the submerged sucker rod pump assembly, which is installed near the bottom of the well. As the beam pumping system reciprocates, this alternately raises and lowers the sucker rod string and operates the sucker rod pump. The pump contains a plunger, barrel and valve assembly to convert the reciprocating motion to vertical fluid movement and lifts the oil from the reservoir through the internal space within the production tubing to the surface.

Sucker rods for use in oil wells are commonly made of steel, typically between 25 and 30 feet (7 to 9 meters) in length, typically ¾ inch to 1⅛ inch diameter and have threaded connections on both ends and are joined end to end to make up a sucker rod string. Steel is used largely because of its high tensile strength however it has the drawback of heavy weight, requiring powerful equipment to raise and lower the sucker rod string within the well. Steel sucker rods are also susceptible to corrosion due to the presence of water and dissolved impurities in the well causing electrochemical reactions between the steel of the sucker rod. The corrosive fluid, in which it is immersed, causes corrosion and stress-corrosion from the axial compressive bending and flexing of the string during the pumping cycle resulting in rod failures.

Fiberglass rods have been used in place of steel rods under certain conditions. These fibreglass rods are normally made from pultruded fibreglass with steel connections bonded with an adhesive resin to each end. These end connections are normally made of steel and have threaded ends, female at one end and male at the other. Fiberglass sucker rods are also commonly available in 37½ foot lengths and typical diameters ranging from of ¾ inch to 1¼ inch.

Fiberglass rods have the advantage that they are more resistant to corrosion and have higher strength to weight ratio and lower rod density than steel sucker rods. The lower weight of the fiberglass rod string allows the use of a smaller pump jack and lower power requirements compared to steel rods. Although fiberglass rods have certain advantages over steel rods, they have some disadvantages. The steel connectors are bonded to the rod body on one surface only and potentially prone to premature failure at this point. Fiberglass rods have poor compressive properties and when the rod string is subject to continual local compression over time due to the cyclical axial loading, premature failure can occur. Local compression can occur if the pump sticks or when the rod goes into compression on the down stroke during the pumping cycle. Fiberglass rods have a finite life dependent on the compressive load, the temperature and number of cycles it is subjected to.

Rod failures reduce economic life of the rod string with periodic replacement required. This requires the rod string to be pulled from the well and each rod inspected and rods with identified faults discarded. This contributes to the cost of oil production as the replacement of a failed rod is a time consuming and expensive process.

Steel and fibreglass rods are commonly manufactured to meet the industry standard API Spec. 11B for sucker rods which specifies performance requirements.

In a situation where the traditional beam pump cannot be easily used due to the challenging nature of the well or fluid, for example heavy crude oil or reservoirs where there is insufficient internal pressure, progressive cavity pumps (PCP) are used for artificial lift. The PCP is essentially a mechanical screw pump. The most common and basic form of PCP is the surface driven PCP where a stator comprised of a steel tubular housing with a bonded elastomeric sleeve lining formed with multiple internal helixes matched to the centrally positioned rotor sits at the end of the production tubing. The rotor is attached to a rod string and rotation of the rod string is through a surface drive system which causes the rotor to spin within the fixed stator, creating the pumping action to pump fluids to surface. The rod string is manufactured from steel and in certain applications hollow steel rod is used in place of a solid string.

The conventional solid steel rods have been developed for an axial load rather than a torsional load as used in the rotation of the rod string of the PCP. The hollow rod assembly allows for a greater torque capacity to be applied during rotation of the PCP compared to a solid steel rod string where cyclical torsional loads presents a greater likelihood of rod failure in a rotary application.

Another current newer technology is the use of a continuous solid rod which removes the need for the many connections required to make up a rod string. They have the advantage of overcoming the potential rod failures associated with multiple connection joints however the joining of sections of continuous rod by welding still has the drawbacks of potential fatigue and corrosion failure at the welded joint. Also continuous rods require specialised transportation with a large spool and special handling equipment.

The operating conditions of the well bore frequently require chemical dosing such as the injection of corrosion inhibitors, scale and wax inhibitors, or diluents to be injected in the case of heavy crude oil, to allow it to be more easily pumped to the surface. The most common method is to run special injection pipes or capillary tubing extending down the well bore by attaching these to the outside of the production tubing. This additional pipe or tubing is time consuming to run and adds additional expense to the operation of the well.

In the case of progressive cavity pumps, chemical dosing and the addition of diluents can be achieved by utilising the hollow core of the steel rod string to inject fluids directly through this into the well. The hollow steel rod string however still has the same inherent drawbacks of high weight and susceptibility to corrosion of a solid steel string.

The present disclosure relates to improved arrangements for and methods and assembly of sucker rods which may overcome disadvantages of known technology related to both a solid rod string and hollow string and which may be suitable for use in both jack pump and progressive cavity pump applications; or to provide the public with a useful choice.

SUMMARY OF THE DISCLOSURE

Various aspects of the invention are defined in the appended claims. These may provide certain advantages including but not limited to the following. An improved hollow sucker rod assembly with reduced weight and corrosion resistance that may overcome the drawbacks of the solid steel rod and fiberglass rod strings for jack pump applications. More efficient well production and a hollow core for fluid injection not achievable with fiberglass rod strings.

More efficient fluid injection efficiency and simplification by removing the need for additional injection pipes and capillaries. A measuring device can be lowered through the hollow core that allows in situ measurements that can be used to identify and mitigate wear and operational issues.

Additionally improved sucker rods according to embodiments of the invention can be used for progressive cavity pump applications.

In accordance with one embodiment there is provided an improved sucker rod assembly consisting of a unitary cylindrical tubular aluminium alloy body with a concentric hollow bore and end connectors. In one or more embodiments, this unitary hollow aluminium body is manufactured by an extrusion process. Each end of the tubular body has a machined male thread form extending a short distance axially from the ends.

In one or more embodiments, aluminium alloy grades 2000, 6000 or 7000 are used. However other grades may alternatively be used.

In one or more embodiments a rod end connector comprises a substantially cylindrical form of greater diameter than the hollow cylindrical tubular body manufactured from steel and coated with an anti-corrosion finish. The rod end connector has a hollow bore formed through the centre of the body concentric with the outer diameter. An internal threaded socket is formed at the cylindrical end of the connector with a female thread form. On the other end of the connector a male screw threaded section is formed on the external diameter to fit with the internally threaded socket of a rod end connector. The threaded male end of the hollow tubular body screws into the internally threaded socket of the end connector where the internal bore of the connector and tubular body lining up concentrically forming a hollow sucker rod assembly. This assembly is fitted to a steel sucker rod coupling where the male end of the connector is attached by its screw thread into the socket of the steel sucker rod coupling. A similarly assembled rod with end connector is attached to the open end of the steel coupling. Multiple rods are connected together in the same manner creating a continuous string with a continuous hollow core. The resulting rod string weight is less than that of an equivalent steel rod string for the same application. In an alternative arrangement the threads may be reverse for example the above described internal threads may instead be externally applied.

The use of separate end connectors allows for simpler production, and the use of steel connectors provides a much stronger connection. In an embodiment the connectors are the same shape as the corresponding end of a standard sucker rod in order to allow standard handling and runner gear to be used. In embodiments the coupling bore is the same diameter as the bores of the connector and hollow sucker tube.

A hollow sucker rod assembly allows for the relatively easy introduction of chemical agents and sensors into the well, without the need for additional conduits. A hollow rod can also handle a greater torsional load compared to a solid rod of the same cross-sectional area. Embodiments may be used in both PCP (progressive cavity pump) and jack-pump oil well applications.

At or proximate the mid point on the coupling in one or more embodiments, one or more holes may be formed into the coupling through the body of the coupling and through to the hollow core, and form a junction at the intersection of it and the hollow core of the connector.

This port(s) provides a connection of the fluid injection apparatus where in one embodiment similarly formed couplings can be inserted at predetermined positions along the rod string to allow the injected fluid to flow outwards into the well or transported through the rod string directly through to the intake of the downhole pump.

The hollow rod string can provide a means of inserting sensor devices for measurement of operating parameters and operation of other powered devices.

Couplings with one or more ports may be included at one or more intermediate positions along a sucker string so that fluid and/or sensors may be introduced at different depths within the well. This avoids the need for additional lines and connected equipment which simplifies operation and reduces costs.

In another aspect there is provided a sucker rod assembly for use in an oil well, the sucker rod assembly comprising an elongated hollow rod having a threaded section at an end, a tubular connector having a threaded section at one end for engaging with the threaded section of the elongated hollow rod, and a second threaded section at the other end, and a tubular coupling having a threaded section at each end for engaging with the second threaded section of said tubular connector and with a second tubular coupling or sucker rod, wherein the hollow rod, connector and coupling form a continuous hollow core for carrying fluid, cables, fibre optics or other materials.

The elongated hollow rod may comprise an aluminum alloy.

The tubular connector may comprise a steel alloy.

The tubular connector may comprise a wrench section and flange, the wrench section having a rectangular cross-section and the other parts of the tubular connector having circular cross-sections.

The continuous hollow core may be the same diameter in each of the hollow rod, tubular connector and tubular coupling.

The sucker rod assembly may comprise a port extending from an external diameter through the wall to the hollow core. The port may be located in the tubular coupling and may comprise a one-way value for delivery of fluid from the hollow core into the oil well.

Alternatively, or additionally a sensor or other equipment may be inserted into the port.

The hollow rod may further comprise a centraliser having a recessed surface pattern arranged to create turbulence in fluid flowing past the centraliser. The recessed surface pattern of the centraliser forms a series of peaks and troughs in longitudinal profile. The recessed surface pattern of the centraliser may comprise channels extending at an acute angle to the longitudinal axis of the hollow rod. The recessed surface pattern of the centraliser may comprise a longitudinally extending intertwined double helix. The centraliser may be tapered at each end. The centraliser may comprise Polyketone.

In another aspect there is provided a hollow sucker rod for use in an oil well, the hollow sucker rod comprising an elongated tubular body of aluminum alloy with a hollow bore, a screw threaded section at each end, and a wrench section and flange, the wrench section having a rectangular cross-section and the other parts of the sucker rod having circular cross-sections.

The hollow sucker rod may further comprise a centraliser having a recessed surface pattern arranged to create turbulence in fluid flowing past the centraliser. The recessed surface pattern of the centraliser forms a series of peaks and troughs in longitudinal profile and comprises channels extending at an acute angle to the longitudinal axis of the hollow rod, the centraliser being tapered at each end. The recessed surface pattern of the centraliser comprises a longitudinally extending intertwined double helix. The centraliser may comprise Polyketone.

In another aspect there is provided a sucker rod string for use in an oil well, the sucker rod string comprising a plurality of hollow sucker rods coupled to each other by tubular couplings to form a continuous hollow core between each end of the suck rod string, and one or more tubular couplings having a port extending from an external diameter through a wall in the sucker rod string to the hollow core. Ports may be located in one or more tubular couplings.

The one or more of the ports may comprise a one-way value for delivery of fluid from the hollow core into the oil well. The one or more of the ports may comprise a sensor, a cable or fibre optic connected to the sensor being run along the hollow core.

The one or more sucker rods may comprise an assembly comprising an elongated hollow rod having an external threaded section at an end, and a tubular connector having an internal threaded section at one end for engaging with the external threaded section of the sucker rod, and an external threaded section at the other end for engaging with a said coupling.

The one or more of the sucker rods comprises an aluminum alloy.

In another aspect there is provided a sucker rod for use in an oil well, the sucker rod comprising an elongated rod having an externally located centraliser which comprises a recessed surface pattern arranged to create turbulence in fluid flowing past the centraliser.

The recessed surface pattern of the centraliser may form a series of peaks and troughs in longitudinal profile. The recessed surface pattern of the centraliser may comprise channels extending at an acute angle to the longitudinal axis of the hollow rod. The recessed surface pattern of the centraliser may comprise a longitudinally extending intertwined double helix.

The centraliser may be tapered at each end. The centraliser may comprise Polyketone.

The elongated rod may be hollow and comprised of aluminum alloy.

In another aspect there is provided a sucker rod for use in an oil well, the sucker rod comprising an elongated rod having an externally located centraliser which comprises Polyketone.

The centraliser may comprise a recessed surface pattern arranged to create turbulence in fluid flowing past the centraliser. The recessed surface pattern of the centraliser may form a series of peaks and troughs in longitudinal profile and comprises channels extending at an acute angle to the longitudinal axis of the hollow rod, the centraliser being tapered at each end. The recessed surface pattern of the centraliser may comprise a longitudinally extending intertwined double helix.

In another aspect there is provided a sucker rod assembly comprising an elongated tubular body of aluminium alloy with a hollow bore having a male external screw threaded section at each end, with each end fitted with a steel connector having an internal female threaded section at one end which screws onto the male threaded section of the tubular body and with a central hollow bore having a diameter equal to the internal diameter of the bore of the elongated tubular body and the opposing end of the connector comprising a male external screw thread.

The assembly may further comprise a sucker rod coupling wherein the coupling has a female threaded internal section at each end where the male thread of the tubular connector is fitted to one of the female thread of the coupling.

The male screw thread of the tubular body may be a buttress thread and the female thread of the connector is a buttress thread.

The coupling may have a port along the longitudinal axis and formed at an angle extending through to its central bore.

The sucker rod assembly may comprise a polymer centraliser on the tubular body. The polymer centraliser may comprise Polyketone. The polymer centraliser may contain one or more additional constituents of glass fibre, carbon fibre, Aramid fibre or graphite. The polymer centraliser may further comprise a recessed surface pattern in the form of an intertwined double helix extending at each end to a taper.

In another aspect there is provided a sucker rod string comprising a plurality of sucker rod assemblies each having a sucker rod coupling wherein the coupling has a female threaded internal section at each end where the male thread of the tubular connector is fitted to one of the female thread of the coupling, the assemblies fitted together wherein the male end of a said sucker rod end connector fits to the female end section a respective said sucker rod coupling.

The coupling may have a port extending from the outer diameter to the inner hollow bore where the port can be either threaded internally or not threaded.

The exposed surfaces of the connector may be coated in an anti-corrosion coating.

The sucker rod assemblies may have a one-way valve is inserted into the coupling to allow the injection of a fluid to flow through the bore of the sucker rod string. A one-way valve may be inserted to allow the injection of a gas to flow through the bore of the sucker rod string.

A fibre optic may be inserted into the coupling and attached to one or more sensor devices.

An electrical cable may be inserted into the coupling and attached to one or more sensor devices. An electrical cable may be inserted into the coupling and attached to a heating device.

A powered sensor may be inserted into the coupling.

A powered data recording device may be inserted into the coupling.

The tubular sucker rod string may be used to drive a jack pump.

The tubular sucker rod string may be used to drive a progressive cavity pump.

In another aspect there is provided a sucker rod for use in an oil well, the sucker rod comprising an elongated hollow rod of aluminum alloy.

Further aspects of the invention, which should be considered in all its novel aspects, will become apparent to those skilled in the art upon reading of the following description which provides at least one example of a practical application of the invention.

DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will be described below by way of example only, and without intending to be limiting, with reference to the following drawings.

FIG. 1 is a side view of the tubular body of the sucker rod showing the male threaded sections at each end.

FIG. 2 is a side view of one end of the tubular body of the sucker rod with attached connector on the one end.

FIG. 2A is a section view of the tubular body.

FIG. 2B is an end view of the connector and tubular body FIG. 3 is a sectional side view of one end of the tubular body and attached connector showing the threaded connection and central bore through the tubular body and connector.

FIG. 4 is a side view of one end of the tubular body of the sucker rod showing the over moulded centraliser and connector.

FIG. 5 is a section view of one end the tubular body of the sucker rod assembly showing the over moulded guide and connector.

FIG. 6 is a 3-dimensional view of one end of a sucker rod assembly with an over moulded centraliser.

FIG. 7 is a solid model of a sucker rod assembly connected together with another sucker rod assembly by a coupling.

FIG. 8 is a section side view of the sucker rod coupling connecting 2 sucker rod assemblies.

FIG. 9 is a side view of the sucker rod coupling with port.

FIG. 10 is a side section view of the sucker rod coupling with port.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In the illustrated embodiment of the invention the sucker rod assembly 3 comprises a unitary tubular body 1 with concentric inner tubular bore 6 with a male screw thread form 2 and end connector 5. The tubular body 1 is coupled by its male screw thread to an end connector 5 with a female threaded internal section 9. The end connector 5 consists of a hollow bore 8 concentric with the general cylindrical form of the connector and extending the full length of the connector.

The diameter of the bore 8 of the connector matches the bore 6 internal diameter of the tubular body 1 and when the tubular body 1 is coupled to the end connector 5 the internal bore 6 and 8 forms a continuous internal bore.

The unitary tubular body 1 in one or more embodiments is formed by an extrusion process that simultaneously forms the concentric bore along the axial length of the tubular body 1 and the outer tubular body has a polished finish. The ends of each tubular body have a machined flat face 11 perpendicular to the longitudinal axis of the tubular body.

The unitary tubular body 1 in one or more embodiments is formed from an aluminium alloy, preferably 2000, 6000 and 7000 series.

In one or more embodiments the tubular body 1 preferably has an outside diameter of 1.25 inches and internal bore 6 diameter of 12 mm and minimum axial tensile pull load of 55,000 lbs. These embodiments matches the tensile load capacity of the common API rated ⅞ in OD grade D rods with a maximum 54,100 lb pull load.

At each end of the tubular body 1, a threaded section 2 extends a short length from each end.

The threaded section comprises a screw thread with preferably a buttress thread form.

The screw threaded section 2 of the tubular body is formed to engage into the internally threaded section 9 of the connector 5, and each thread engages to form a tightly coupled and sealed connection. The female internally thread section 9 of the connector is preferably a buttress thread form to match the male thread form of the screw threaded section 2.

The end face 11 of the threaded section 2 of the tubular body engages and seals against the corresponding flat internal landing 22 of the internal threaded section 9 of the connector 5.

In one or more embodiments the connector 5 is a unitary body formed from 4140 steel alloy and in another embodiment where additional corrosion resistance is required the unitary body is preferably formed from a NACE MR0175 compliant steel alloy. Preferably the connector 5 has a hollow bore 8 extending axially and concentric with the outer diameter through the length of the connector. Preferable the diameter of this bore is in the range 8 mm to 12 mm and formed to match the internal bore 6 diameter of the tubular body 1.

In one or more embodiments the exposed surfaces of the connector 5 may be coated with an anti-corrosion coating.

In one or more embodiments the exposed surfaces of the connector 5 may be treated to provide a corrosion resistant finish.

In one or more embodiments the unitary connector 5 comprises a cylindrical section 13, which has an internally threaded section 9 with a female screw thread form 7 is preferably a buttress thread. Adjacent to the cylindrical section is a section with four equal rectangular flat faces 4 formed into a section of the cylindrical body forming a square section 15 as shown in FIG. 6. Directly adjacent to this is a flange section 14. This square section allows for the placement of a wrench or gripping tool to grip the connector so that it remains stationary while a coupling 20 or another sucker rod assembly is fitted together. The flange section 14 extends to a cylindrical section with a formed male threaded section with an industry standard API connection screw thread. This male threaded portion threads into the female threaded section 21 of an industry standard coupling.

When the tubular body 1 is coupled to the unitary connector 5, the internal bore of each component is fully aligned with each other forming a sucker rod assembly 3 with a continuous hollow bore through both components as shown in the section view of FIG. 3. This assembly 3 is attached to a coupling 20 by the threaded end of the connector 10 and the opposing end attaches by the thread 21 to the end of another assembly 3. Multiple sucker rod assemblies are interconnected in this manner to form a continuous sucker rod string with a continuous hollow core.

In another embodiment one end of the tubular body 1 may be formed by an upset forging operation to create an upset end where the end section of one end of the tubular body 1 is greater than the original diameter. An internal female screw thread is then formed in the upset section to fit the screw thread section 2.

In one or more embodiments the coupling 20 may have a port 23 extending from the outer surface of the cylindrical section of the coupling 20 through perpendicular to the central hollow core. The port 23 in one embodiment may have a smooth bore.

The port 23 in one embodiment is preferably perpendicular to the axis of the hollow core but can be formed at any other preferred angle and position with the coupling 20.

This port 23 in another embodiment has a threaded section to fit a one way valve. This provides an injection port to allow the injection of chemicals or fluids through the one way valve into the hollow core and transported to the end of the rod string or any position within the string where a corresponding connector with an open port 23 allows the expelling of the injected chemical or fluid into the well bore. Preferably the injection chemical may include but not limited to acids, alkalis, corrosion inhibitors, anti wax chemicals, anti scaling chemicals and diluents.

Preferably the coupling 20 with port 23 is assembled at predetermined points along the length of the rod string to allow chemical dosing at various positions within the well bore.

In another embodiment the injection of fluids may be transported from one or more port 23 at the top section of the rod string through the hollow bore to the bottom of the well to the intake of a suitably modified downhole pump which disperses the fluid.

In one or more embodiments the port 23 may be used at the surface for the insertion of electrical, data or fibre optic cable connected to one or more sensors that are pushed or blown down through the hollow core 6 & 8 extending partially or to the end of the rod string at the base of the well. These sensors or devices whether powered or passive are preferably used to monitor well conditions and include but not limited to pressure sensors, temperature sensors, accelerometers, data recorders and strain gauges at one or more positions along the rod string.

These sensors or devices may incorporate mechanisms that latch to the power and or data connection cables temporarily or to connect latch these permanently.

In another implementation, the sensor device may be incorporated within the coupling 5 itself.

In another embodiment the hollow rod string may be used to insert and power a heating device to reduce the viscosity of the well fluid to enable more efficient pumping.

The sucker rod assembly 3 is preferably produced in industry standard lengths however rod assemblies of shorter lengths can be utilised where the tubular body 10 is produced in a shorter length. These shorter rods can be used to make up a rod string to a specific total length.

To prevent the tubular rod from contacting the inner wall of the steel production tube with the potential for abrasive wear to occur on the body of the tubular body, in one or more embodiments the tubular rod assembly may comprise of a polymer centraliser 16 over moulded onto the external surface of the tubular body 1 a predetermined distance away along the outer surface from the connector 5. The polymer centraliser preferably comprises a polyketone and in one or more embodiments may contain a material of glass, graphite, carbon or aramid fibre, and in any proportion. Friction modifiers may additionally be added to modify the friction properties of the polymer. The external diameter of the over moulded centraliser being greater than the diameter of the coupling 20 but less than the internal diameter of the production tube.

The combination of a polyketone centraliser and aluminium alloy rod provides reduced friction and reduced weight thereby reducing the pump drive requirements, and hence reducing both capital and operational costs.

The centraliser 16 preferably on its main body has a plurality of formed helical groves in the form of an intertwined double helix along its length and extending to a taper at each end.

Other embodiments may include modified centraliser shapes, for example with a reduced number of grooves. These and other embodiments can produce a more turbulent flow of fluid up the well compared with known centraliser arrangements. The turbulent flow can move the liquid with its corrosive components more quickly past the sucker rod string parts therefore reducing their exposure to these corrosive elements, and hence extending their life. The more turbulent from will also reduce the size and formation of gas bubbles (especially CO2 and H2S) which reduces the occurrence of cavitation corrosion. More generally the centraliser keeps the sucker string well centred in the oil well, reducing component stress and wear.

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to”.

The entire disclosures of all applications, patents and publications cited above and below, if any, are herein incorporated by reference.

Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavour in any country in the world.

The invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features.

Where in the foregoing description reference has been made to integers or components having known equivalents thereof, those integers are herein incorporated as if individually set forth.

It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be included within the present invention. 

What is claimed is:
 1. A sucker rod assembly for use in an oil well, the sucker rod assembly comprising: an elongated hollow rod having a threaded section at an end; a tubular connector having a threaded section at one end for engaging with the threaded section of the elongated hollow rod, and a second threaded section at the other end; and a tubular coupling having a threaded section at each end for engaging with the second threaded section of said tubular connector and with a second tubular coupling or sucker rod, wherein the hollow rod, connector and coupling form a continuous hollow core for carrying fluid, cables, fibre optics or other materials.
 2. The sucker rod assembly of claim 1, wherein the elongated hollow rod comprises an aluminum alloy.
 3. The sucker rod assembly of claim 2, wherein the tubular connector comprises a steel alloy.
 4. The sucker rod assembly of claim 1, wherein the tubular connector comprises a wrench section and flange, the wrench section having a rectangular cross-section and the other parts of the tubular connector having circular cross-sections.
 5. The sucker rod assembly of claim 1, wherein the continuous hollow core is the same diameter in each of the hollow rod, tubular connector and tubular coupling.
 6. The sucker rod assembly of claim 1, wherein the sucker rod assembly comprises one or more ports extending from an external diameter through a wall to the hollow core.
 7. The sucker rod assembly of claim 6, wherein the or each port is located in the tubular coupling.
 8. The sucker rod assembly of claim 6, wherein a said port comprises a one-way value for delivery of fluid from the hollow core into the oil well.
 9. The sucker rod assembly of claim 6, further comprising a sensor or other equipment inserted into a said port.
 10. The sucker rod assembly of claim 1, wherein the hollow rod further comprises a centraliser having a recessed surface pattern arranged to create turbulence in fluid flowing past the centraliser, wherein the recessed surface pattern of the centraliser forms a series of peaks and troughs in longitudinal profile.
 11. The sucker rod assembly of claim 10, wherein the recessed surface pattern of the centraliser comprises channels extending at an acute angle to the longitudinal axis of the hollow rod.
 12. The sucker rod assembly of claim 11, wherein the recessed surface pattern of the centraliser comprises a longitudinally extending intertwined double helix.
 13. The sucker rod assembly of claim 12, wherein the centraliser is tapered at each end.
 14. The sucker rod assembly of claim 9, wherein the centraliser comprises Polyketone.
 15. A sucker rod string for use in an oil well, the sucker rod string comprising: a plurality of elongated hollow rods each having a threaded section at an end; a plurality of tubular connectors, each having a threaded section at one end for engaging with the threaded section of a respective elongated hollow rod and a second threaded section at the other end; a plurality of tubular couplings, each having a threaded section at each end of the tubular coupling for engaging with the second threaded section of a respective tubular connector in order to couple the sucker rods together to form a continuous hollow core between each end of the sucker rod string for carrying fluid, cables, fibre optics or other materials.
 16. The sucker rod string of claim 15, further comprising a number of ports extending from an external diameter through a wall to the hollow core.
 17. The sucker rod string of claim 16, wherein one or more of the ports comprise a one-way value for delivery of fluid from the hollow core into the oil well at intermediate locations along the sucker rod string.
 18. The sucker rod string of claim 15, wherein the elongated hollow rods comprise an aluminum alloy.
 19. The sucker rod string of claim 18, wherein the tubular connectors comprise a steel alloy.
 20. The sucker rod string of claim 15 connected to a jack pump or a progressive cavity pump. 